Environmental constraints on sound transmission by humpback whales

Singing humpback whales in Hawaii produce a variety of sounds at high source levels (ca. 185 dB re: 1 mu Pa), in coastal waters 15-500 m deep. These sounds are attenuated and distorted as they propagate away from a singer, limiting the utilizable range of the sounds. In the current study, simulations based on normal-mode theory were used to investigate how the effects of shallow-water propagation constrain humpback whales' use of sound. It is shown that humpbacks can greatly affect transmission range by adjusting their positions and sounds in response to environmental factors. Source depth, in particular, is shown to be a major determinant of which frequencies propagate the farthest, A preliminary analysis of range-dependent distortion suggests that spectral cues can potentially provide listening whales with information about how far a sound has traveled. (C) 1999 Acoustical Society of America. [S0001-4966(99)01211-4].